To access the computer system, an
employee must insert his smart card into a reader/
writer device and enter his unique
PIN via the reader/writer's keyboard. The smart
card's microcomputer chip then performs
the same one-way transformation on the
entered PIN and compares it with the
stored PIN. Because this comparison is done
completely inside the smart card's
microcomputer chip, the employee's PIN is never
written into the open working memory
of the host computer, which might be exposed
to modification or monitoring by
an adversary.
If the smart card determines that
the two PINs match, information is exchanged
between the smart card and the host
computer to determine the employee's identity
and which files within the host the
employee is entitled to access. The employee can
then read and update only those files
via a terminal connected to the host computer.
A log of the employee's actions within
the computer system can be maintained within
the smart card's memories.
1.0
SMART
CARD INTEGRATED CIRCUIT TECHNOLOGIES
The smart card's ability to perform
the computations and other functions needed in
security applications depends on the
development of the smart card microcomputer, which,in turn, is inherently tied
to the progress of integrated circuit technologies. This chapterdiscusses some of
the concepts and considerations involved in the production of integrated circuits.
1.1
Integrated
Circuits (ICs)
Integrated circuits (ICs) are electronic
circuits, of varying complexity, which are
formed on individual chips of silicon
(or other semiconductor* material). Computers and digital instruments are filled
with ICs, which are small and can be designed to quickly perform complicated functions.
The capability of an IC depends
on the amount of circuitry it contains, a quantity
often described in terms of transistor
density. With current IC technology, close to 400
transistors can be formed in a
space as small as the cross-section of a human hair, which is approximately 100
microns (millionths of a meter) in diameter. With this transistor density, ICs
containing about 50,000 transistors can be produced; transistors are placed on
an integrated circuit and interconnected with "wires" 1 micron in width.
If this "wire" width were reduced to half a micron, 1500 transistors could
be placed in a 100-micron cross-sectional area. Cutting the dimensions in half again
would make each transistor the size of a large virus. With quarter micron "wire"
widths, 4500 transistors could be placed in the cross-sectional area of a hair.
It is predicted that the latter capability may be reached by 1995 .
Some sources believe that with the
increases in transistor density, the billion-transistor
IC will become a definite reality
by the year 2000. [COLE 87, p. 81] If an estimated
200,000 transistors are needed to
store and handle one page of text, a billion-transistor
IC could store several thousand printed
pages. Any of these pages could be retrieved in arandom fashion from such a supercircuit
and transmitted between two computers in abouta second.
It is important to realize, however,
that as the density of transistors in ICs increases,
so does the difficulty of producing
ICs that function correctly. If a single transistor in any part of an IC fails,
the operation of the entire IC chip may be impaired.
1.2
Limitations
of IC Technology
Simply stated,
the goal of IC technology is to produce reliable ICs which are reduced in size and
yet increased in capability. The extent to which this goal can be attained is limited
by the physical characteristics of the materials used for both the substrate (the
foundation for the IC) and the actual circuitry to be placed on that substrate.
All silicon materials used to produce IC substrates have a certain defect density.
The IC fabrication engineer must work within the limitation that, in a given section
of silicon substrate material, there will be a certain number of defects. If this
section is cut into a small number of large chips, a high percentage of the chips
produced will contain one or more defects. However,if the section is cut into a
large number of small chips, a much lower percentage of the chips produced will
contain defects. The chips produced must be both large enough to accomodate the
circuitry to be placed on them and yet small enough that a reasonable yield of usable
chips can be produced from each section of silicon substrate.In order to increase
the amount of circuitry which can be placed on a small silicon chip,the circuits
themselves are made smaller. Much research is devoted to methods for reducing linewidth,
the amount of space needed by an interconnecting "wire." Some sources
predict that the conventional method (optical lithography) can be pushed to produce
circuits with 0.1 micron linewidths. This would constitute a 5 to 10 times improvement
over current capabilities. [COLE 87, p. 83] The smaller reliable circuitry can
be made, the more functions each chip can support.In addition to reducing linewidth,
current research efforts are aiming towards the production of application-specific
ICs (ASICs), partially customized ICs which are fabricated according to standard
conventions. The increase in IC functionality, made possible by reduced linewidth
and custom fabrication, will be of primary importance in the development of microcomputer
chips such as those used in smart cards.
2.0
THE
SMART CARD MICROCOMPUTER
The word microcomputer is typically
used to mean simply a "small" computer. Within
the category of "small"
computers there is a very wide variety of devices, ranging from
a personal computer (which may be
equipped with such peripherals as a monitor, a keyboard,one or more floppy disk
drives, a hard disk, a mouse, a modem, a printer, and/or others) down to an IC chip
no larger than an eraser on the end of a pencil. Microcomputers may diff"er
greatly in their costs, capabilities, and intended applications. In general,
however, each microcomputer is comprised
of three basic components: a microprocessor
(for managing information), memory
(for storing information), and an input/output (I/O)interface (for transmitting
and receiving information).
The desktop personal computer is one
of the most common types of microcomputer.
A personal computer may contain dozens
of integrated circuits; usually one IC forms
the microprocessor, a large number
of ICs serve as memory, and a few ICs control the
input/output interface. Because they
are so small and because they are designed for
different applications, smart cards
do not contain all of the integrated circuitry that is
housed within personal computers.
Smart cards do, however, contain all three of the basic microcomputer
components.
Researchers and manufacturers
have developed many different designs for the tiny
microcomputer to be placed in a smart
card. A fundamental issue in smart card design
is whether the microcomputer should
be restricted to a single IC chip or distributed over several chips.
